Kernel Source片段 -- bridge的處理

kernel version：2.6.32.61

在netif_receive_skb中會調用橋處理函數handle_bridge進行橋相關處理。

net/core/dev.c

2151 static inline struct sk_buff *handle_bridge(struct sk_buff *skb,
2152                                             struct packet_type **pt_prev, int *ret,
2153                                             struct net_device *orig_dev)
2154 {
2155         struct net_bridge_port *port;
2156         
2157         if (skb->pkt_type == PACKET_LOOPBACK || 
2158             (port = rcu_dereference(skb->dev->br_port)) == NULL)
2159                 return skb;
2160                      
2161         if (*pt_prev) { 
2162                 *ret = deliver_skb(skb, *pt_prev, orig_dev);
2163                 *pt_prev = NULL;
2164         }       
2165         
2166         return br_handle_frame_hook(port, skb);
2167 }

主要處理是在br_handle_frame_hook中進行的，而br_handle_frame_hook是在br_init中進行的。

net/bridge/br.c

 35 static int __init br_init(void)
 36 {
 37         int err;
 38 
 39         err = stp_proto_register(&br_stp_proto);
 40         if (err < 0) {
 41                 printk(KERN_ERR "bridge: can't register sap for STP\n");
 42                 return err;
 43         }
 44 
 // 使用SLAB，初始化fdb
 45         err = br_fdb_init();
 46         if (err)
 47                 goto err_out;
 48 
 49         err = register_pernet_subsys(&br_net_ops);
 50         if (err)
 51                 goto err_out1;
 52 
// 初始化橋的netfilter
 53         err = br_netfilter_init();
 54         if (err)
 55                 goto err_out2;
 56 
// 註冊通知鏈
 57         err = register_netdevice_notifier(&br_device_notifier);
 58         if (err)
 59                 goto err_out3;
 60 
// netlink初始化
 61         err = br_netlink_init();
 62         if (err)
 63                 goto err_out4;
 64 
 65         brioctl_set(br_ioctl_deviceless_stub);
// 初始化br_handle_frame_hook 
 66         br_handle_frame_hook = br_handle_frame;
 67 
 68 #if defined(CONFIG_ATM_LANE) || defined(CONFIG_ATM_LANE_MODULE)
 69         br_fdb_test_addr_hook = br_fdb_test_addr;
 70 #endif
 71 
 72         return 0;
 73 err_out4:
 74         unregister_netdevice_notifier(&br_device_notifier);
 75 err_out3:
 76         br_netfilter_fini();
 77 err_out2:
 78         unregister_pernet_subsys(&br_net_ops);
 79 err_out1:
 80         br_fdb_fini();
 81 err_out:
 82         stp_proto_unregister(&br_stp_proto);
 83         return err;
 84 }

在br_handle_frame中，區分了本地包和轉發包。主要的處理集中在
162                 NF_HOOK(PF_BRIDGE, NF_BR_PRE_ROUTING, skb, skb->dev, NULL,
163                         br_handle_frame_finish);

代碼如下：
net/bridge/br_input.c

120 struct sk_buff *br_handle_frame(struct net_bridge_port *p, struct sk_buff *skb)
121 {
122         const unsigned char *dest = eth_hdr(skb)->h_dest;
123         int (*rhook)(struct sk_buff *skb);
124 
125         if (!is_valid_ether_addr(eth_hdr(skb)->h_source))
126                 goto drop;
127 
128         skb = skb_share_check(skb, GFP_ATOMIC);
129         if (!skb)
130                 return NULL;
131 
132         if (unlikely(is_link_local(dest))) {
133                 /* Pause frames shouldn't be passed up by driver anyway */
134                 if (skb->protocol == htons(ETH_P_PAUSE))
135                         goto drop;
136 
137                 /* If STP is turned off, then forward */
138                 if (p->br->stp_enabled == BR_NO_STP && dest[5] == 0)
139                         goto forward;
140 
141                 if (NF_HOOK(PF_BRIDGE, NF_BR_LOCAL_IN, skb, skb->dev,
142                             NULL, br_handle_local_finish))
143                         return NULL;    /* frame consumed by filter */
144                 else
145                         return skb;     /* continue processing */
146         }
147 
148 forward:
149         switch (p->state) {
150         case BR_STATE_FORWARDING:
151                 rhook = rcu_dereference(br_should_route_hook);
152                 if (rhook != NULL) {
153                         if (rhook(skb))
154                                 return skb;
155                         dest = eth_hdr(skb)->h_dest;
156                 }
// 注意此處沒有break
157                 /* fall through */
158         case BR_STATE_LEARNING:
159                 if (!compare_ether_addr(p->br->dev->dev_addr, dest))
160                         skb->pkt_type = PACKET_HOST;
161 
162                 NF_HOOK(PF_BRIDGE, NF_BR_PRE_ROUTING, skb, skb->dev, NULL,
163                         br_handle_frame_finish);
164                 break;
165         default:
166 drop:
167                 kfree_skb(skb);
168         }
169         return NULL;
170 }

在走過橋的NF_BR_PRE_ROUTING的hook點之後，就進入了br_handle_frame_finish中。
這裏首先更新了fdb，然後根據fdb查找結果決定直接轉發還是flood轉發。
這裏還有需要注意的是br_pass_frame_up會將包的dev改成橋，然後重新進入netif_receive_skb。

net/bridge/br_input.c

 38 int br_handle_frame_finish(struct sk_buff *skb)
 39 {
 40         const unsigned char *dest = eth_hdr(skb)->h_dest;
 41         struct net_bridge_port *p = rcu_dereference(skb->dev->br_port);
 42         struct net_bridge *br;
 43         struct net_bridge_fdb_entry *dst;
 44         struct sk_buff *skb2;
 45 
 46         if (!p || p->state == BR_STATE_DISABLED)
 47                 goto drop;
 48 
 49         /* insert into forwarding database after filtering to avoid spoofing */
 50         br = p->br;
// 更新fdb
 51         br_fdb_update(br, p, eth_hdr(skb)->h_source);
 52 
 53         if (p->state == BR_STATE_LEARNING)
 54                 goto drop;
 55 
 56         /* The packet skb2 goes to the local host (NULL to skip). */
 57         skb2 = NULL;
 58 
 59         if (br->dev->flags & IFF_PROMISC)
 60                 skb2 = skb;
 61 
 62         dst = NULL;
 63 
 64         if (is_multicast_ether_addr(dest)) {
 65                 br->dev->stats.multicast++;
 66                 skb2 = skb;
 67         } else if ((dst = __br_fdb_get(br, dest)) && dst->is_local) {
 68                 skb2 = skb;
 69                 /* Do not forward the packet since it's local. */
 70                 skb = NULL;
 71         }
 72 
 73         if (skb2 == skb)
 74                 skb2 = skb_clone(skb, GFP_ATOMIC);
 75 
 76         if (skb2)
// 將dev改爲橋，發往netif_receive_skb
 77                 br_pass_frame_up(br, skb2);
 78 
 79         if (skb) {
 80                 if (dst)
// 轉發到學習到的對應端口
 81                         br_forward(dst->dst, skb);
 82                 else
// flood轉發
 83                         br_flood_forward(br, skb);
 84         }
 85 
 86 out:
 87         return 0;
 88 drop:
 89         kfree_skb(skb);
 90         goto out;
 91 }